A tension leg platform (“TLP”) is a vertically moored floating structure used for offshore oil and gas production. The TLP is permanently moored by groups of tethers, called a tension leg, that eliminate virtually all vertical motion of the TLP. As a result of the minimal vertical motion of the TLP, the production wellhead may be located on deck instead of on the seafloor. The production wellhead connects to a subsea wellhead by one or more rigid risers.
The risers that connect the production wellhead to the subsea wellhead can be thousands of feet long and extremely heavy. To prevent the risers from buckling under their own weight or placing too much stress on the subsea wellhead, upward tension is applied, or the riser is lifted, to relieve a portion of the weight of the riser. The risers between the surface and the mudline and the risers in the well are supported by the surface platform. Thus, the surface wellhead must be very large and complex so that it may support the full weight of the risers.